The Hay group analyzed 8.7 million employees across 33 countries, the above being on page 8 of their methodology report ~~(which I unfortunately don't have a current link to, since it looks like their website structure changed since I last checked it out, I was only able to find the white paper)~~, to find the real figures behind the ‘headline’ gender pay gap that crudely takes the average of all working women’s salaries and compares it to the average of all working men’s salaries, with no context.

The rightmost column shows the pay gap that remains when you compare only men and women working in the same company, at the same level, with the same title. A 1.6% average gap that takes into account NONE of the 20 bullet points in my previous comment. That's the starting point. Even if we assumed ALL of that gap was caused by sexism, a 1.6% difference isn't exactly the Colossus of Misogyny that's been assumed to exist.

Though this is all actually an attempt to 'prove the negative'. As I mentioned before, this is a God of the Gaps argument on the part of people who see this earnings gap between the sexes and assume sexism is the one and only cause of all of it. It's on the people pushing that narrative to show evidence of that, not to just claim that any unaccounted for gap is to be assumed to be caused by sexism.